The perception of a visual "figure" often relies upon the overall spatial arrangement of its local elements. The global attributes of a visual stimulus can affect the response of visual cortical neurons to the local attributes of the stimulus. Thus, the response of early visual cortical neurons to stimuli within their classical receptive field (cRF) can be modulated by contextual stimuli outside their cR. Fast interactions beyond the cRF are needed to mediate these modulatory effects. The long-term goal of this proposal is to disentangle the relative contributions of inter-areal (feedforward and feedback) and intra-areal horizontal corticocortical connections to these global-to-local interactions in early visual cortex. The neural circuitry and mechanisms involved are likely to be the cornerstone of contour integration, and figure-ground segregation. Thus, results from these studies ultimately will help understanding the neural substrates for higher visual cortical processing and perception in primate and man. The work described in this application is designed to investigate how the spatial extent and functional specificity of intra-areal and inter-areal connections in cortical areas V1, V2 and V3 relates to the spatial scale and functional specificity of single V1, V2 and V3 neurons responses to stimuli within and beyond their cRF. We will determine the visuotopic extent of the intra- and inter-areal fields of connections labeled by small tracer injections delivered to specific functional compartments of areas V2 and V3 in the marmoset monkey. The visuotopic scale of each connectional system will then be compared to the spatial dimensions of single V1, V2 and V3 neurons' cRF and non-cRF responses, determined by single unit recordings. We will use combined optical imaging and tracer injections to determine whether each of the connectional system is organized in a patterned or diffuse fashion, and how specific connectional patterns relate to the underlying feature maps and functional compartments of early visual cortical areas.